1. Field of the Invention
The present invention relates to an inkjet printing method and an inkjet printing apparatus.
2. Description of the Related Art
A large number of inkjet printing apparatus are available today which realize a high level of image fastness by using a water-based dispersion pigment ink (hereinafter referred to simply as a “pigment ink”). Materials printed with a pigment ink, though excellent in water fastness and light fastness or image fastness, have a drawback that the printed images lack glossiness. This is because the pigment ink does not penetrate deep into the print medium and easily fixes on the print medium surface, thus tending to form undulations on the surface and degrade the smoothness of image surface. In recent years, therefore, there has been a growing call for an inkjet printing technology that can improve the glossiness of image as well as the image fastness.
Japanese Patent Laid-Open No. 2002-144551 discloses a technology whereby a transparent resin (clear ink) is used in addition to the pigment ink for image printing and applied to an area printed with the pigment ink to improve the image fastness and the glossiness of the printed material.
Further, Japanese Patent Laid-Open No. 2004-059933 discloses a technology that improves the glossiness of a non-printed area that is not applied with the pigment ink, by applying a clear ink containing a pore-closing polymer to a porous or semi-porous print medium. With Japanese Patent Laid-Open No. 2004-059933, if the print medium is not glossy, such as plain paper, it is possible to produce a printed material as if the print medium itself is glossy.
Further, Japanese Patent Laid-Open No. 2002-200743 discloses a method of applying the clear ink to an entire image area after it has been printed. Another Japanese Patent Laid-Open No. 2006-272934 discloses a technology that applies the clear ink to the entire image area, as with Japanese Patent Laid-Open No. 2002-200743, and which changes the amount of clear ink applied from one area to another according to the amount of pigment ink applied. More specifically, the volume of clear ink to be applied is reduced in areas where a large volume of pigment ink has been applied, while the clear ink volume is increased where the volume of pigment ink applied is small, thereby aiming to produce a uniform glossiness over the entire image area including non-printed areas and printed areas.
It is, however, still difficult to realize a uniform glossiness over the entire image area including printed areas and non-printed areas, even with any of the above technologies.
The method of Japanese Patent Laid-Open No. 2002-144551, for example, applies the clear ink only to the areas printed with the pigment ink, so the glossiness in the non-printed areas that are not applied with the pigment ink cannot be improved. That is, if the print medium itself does not have a glossiness, it is not possible to produce a printed material having a glossiness over the entire image. Conversely, with Japanese Patent Laid-Open No. 2004-059933, since the clear ink is not applied to the areas printed with the pigment ink, the undulations in the printed area can not be removed. That is, whether the clear ink is applied only to the printed areas, as in Japanese Patent Laid-Open No. 2002-144551, or only to the non-printed areas, as in Japanese Patent Laid-Open No. 2004-059933, a uniform glossiness cannot be obtained over the entire image area including the printed areas and the non-printed areas.
As for the methods disclosed in Japanese Patent Laid-Open Nos. 2002-200743 and 2006-272934, since the clear ink is applied both to the printed areas and the non-printed areas, the glossiness of the entire image area can be expected to be improved. However, even with these methods, since the state of clear ink penetration into the surface of a print medium differs between a position where the pigment ink has been applied and a position not applied with the pigment ink, the undulations in the entire image area are not corrected enough, resulting in a poor glossiness.
The inks that can be used on inkjet printers, including clear ink, can generally be classified into a high-penetrative ink that can easily penetrate into a print medium and a low-penetrative ink that tends to remain on the surface of the print medium for a relatively long time. If the clear ink used is a highly penetrative ink, it forms an appropriate film layer over a pigment ink layer in the areas that have already been printed with the pigment ink, whereas it is quickly absorbed into the print medium in non-printed areas where the pigment ink has not been applied. That is, although the glossiness can be improved in the printed areas, the glossiness improvement cannot be obtained in the non-printed areas.
If, on the other hand, the clear ink is a low-penetrative ink, it forms an appropriate film layer and fixes on the print medium in the non-printed areas. But in the printed areas, the clear ink accumulates on top of the pigment ink, forming additional undulations on the print medium surface. Therefore, although the clear ink can improve the glossiness in the non-printed areas, it degrades the glossiness in the printed areas.
In other words, it has been difficult for an inkjet printing apparatus using a clear ink to produce a printed material that realizes equal levels of smoothness both in the printed areas applied with the pigment ink and in the non-printed areas not applied with the pigment ink and also a uniform glossiness over the entire image formed.